These are the places I've been and what I thought.
Okay, when I was 11 (1999), mum and dad sprung a surprise trip on me and my sister. We went then cos it was just before I turned 12, so the airfare was cheaper. We flew to the US, landing in Salt Lake City. From there we hired a car and drove out way around the landmarks - Grand Canyon, Yellowstone National Park, Monument Valley, etc. Took a week. Was VERY cool. We stopped enough that us two kids didn't get bored (my sister was 10), but covered lots of ground too (2000 miles in 6 days - my dad likes to drive).
Then we flew to Washington DC - mixed feelings about that one. The Smithsonian museums are amazing - so worth a look! And we did a cool night tour of the monuments and stuff. But the thing is, it has a very clear right/wrong side of the tracks. Our hotel was half a block on the wrong side of the tracks, and you could SO tell. The hotel stuffed up our booking, the tiny little corner store had HUGE bars on the windows, and my dad nearly got mugged picking up Chinese take away. It's also one of the most polluted areas I've ever been to. We were there 2 days.
Then we flew to Holland, cos we have family there. That was fantastic, really beautiful. I loved Amsterdam andthe canals and stuff, and we went to a cool zoo. There for a week.
Then we flew back to the US, to Disney World Florida, which is the biggest Disney theme park. We stayed at one of their resorts, and did a different part of the park each day. It was really good, because we had a little card that functioned as our park ticket, room key, and a credit card for food at the resort. That was awesome, cos it meant that mum and dad could go out at night if they wanted, and leave me an my sister with our card to get food and get into the room, and the pool and stuff. It was really fun, they have stuff for all ages. Beware though - it's big. We were there 6 days, we saw about half of what they have. We also spent a day at the Kenedy Space Centre down the road - that was cool.
Based on my experience being a kid on holidays, I'd say the key to travelling with kids is doing enough stuff that they don't get bored. My parents would have loved to just drive around looking at scenery, but we stopped at different things all the time, like dinosaur museums and volcanic springs and stuff. Plus Disney World was the last thing we did, so of course we were on our best behaviour until we got there.
I think mum and dad were lucky cos we were both old enough and interested enough to like museums and stuff, so we were easier to entertain. You'd have to customise it to your kids.
Then last year I went on student exchange after I finished high school. I went to Germany - Colonge/Dusseldorf area, near Holland. But cos it's Europe and everything's so close, I travelled a lot.
In Germany, pretty much every town you visit has something to offer, by way of a 1000 year old cathedral or a famous market or an interesting museum. I did Berlin and Munich as my major trips, both beautiful, but in very different ways. If you go to Berlin, check out KaDeWe, Kaufhaus Des Westerns, the biggest shop in Europe. Also I did an amazing tour of the underground - there was a door in the subway that everyone assumed was a cleaning cupboard until they realised it was never used. They prised it open and discovered a huge, intact WW2 bunker. Very cool. If you end up in Munich, you can't miss Neuschwanstein, the original fairy castle. It's a day trip, but it's SO worth it!!! Also do the film studios and the market place.
I went to Holland again to visit the rellies, and spent a bit more time wandering around Amsterdam. It's one of my favourite places in the world. But I have second thoughts about kids in Amsterdam, even though I first went there when I was 11. You need to remember that marijuana and prostitution are both legal in Holland, and the Amsterdam red light district is a major tourist attraction. Don't enter it unless you are prepared to see censored shops left right and centre (though it is an interesting place too, with a cool old church in the middle). Be careful about which cafes you choose, because some cater specifically to people who want to smoke pot and drink coffee. I loved it though cos it's so normal there - my uncle was giving me a tour, he's like "This is a beautiful old building, 700 years old. You can buy great weed there. Here's a very famous church, where lots of prostitutes do business." Hilarious! It's an amazingly beautiful city too, built along concentric canals. I HIGHLY recommend, I'm just hesitant to label it "kid friendly".
Rome is cool, wall to wall landmarks. Though the churches do get a little overwhelming - they're all so spectacular that it gets boring. Also the Sistine Chapel is a waste of time - it's not nearly as good looking as the rest of the place, and it's crowded and dark, and you have to wait hours to get in. The food is great though, very easy to do on a budget (I had like no money while I was there). I like the character of the city, too.
Paris is lovely, but hard to do on foot. The Eiffel Tower is worth it, though prepare to be homesick if you've been away long, cos up the top it tells you exactly how many kms to various cities, including Canberra and Sydney. It's pricey, but you can argue it cheaper if you want. If you know a second language though, try that before you speak in English. They hate the English and Americans, and if you speak English, they'll be rude to you. I didn't speak any French, but I tried German before English, and people were much nicer and more helpful to me that way. Do the Louvre properly - I was only there for one day, so I chose not to go at all, because I wanted to do it all sometime later. A friend of mine went, but it was so rushed that they saw almost nothing.
London was fantastic. I loved it so much, but that was probably just cos I'm a theatre nut an I got to see Shakespeare's Titus Andronicus at The Globe Theatre (cheapest theatre in London! 5 pounds!) It was also refreshing to speak English and be understood. Also salt and vinegar chips, which it seems can't be bought on mainland Europe.
It's a great city to wander around though, I really liked it.
At the end of last year, Rock Eisteddfod invited me to go to Japan with them. We spent a week in Tokyo, looking around and rehearsing, then performed, then spent another week touring around Tokyo. It's soo busy! Soo many people! But they're all really nice and considerate too. Trains at peak time are scary, and would be tricky with kids, I think. I was in a group of 50 - it wasn't easy!!! Do all the shopping districts like Shiboya(sp?), and find the temples and gardens too cos they're spectacular. We did Disneyland and Disney Sea - not as good as Disney World, but very fun. Tokyo Tower isn't worth it, but the very tall skyscrapers are! We also went to a hot springs theme park near mt Fuji where we could bathe in things like red wine and charcoal and coffee. It was sooo cool! Tokyo is an awesome place!!!
And that is The World According to Me!!!
Have fun on your trip!!!